JP2765602B2 - Auto drift cancellation circuit of ECG analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrocardiogram input method for a portable electrocardiogram analyzer, and more particularly to an auto drift cancel circuit.

[0002]

2. Description of the Related Art A conventional portable electrocardiogram analyzing apparatus has a differential amplifier in an electrocardiogram input section in order to detect and amplify a small electrocardiogram signal derived from an electrode worn by a subject.
The electrocardiogram signal amplified by about 5 times by this differential amplifier passes through a primary filter for cutting its own frequency component (0.05 Hz or less), and is then amplified to about 250 times by the next stage main amplifier. And input to the A / D converter.

[0003]

However, in the conventional portable electrocardiogram analyzer, the power supply voltage during the operation of the amplifier section of the device is about 4 to 6 V because the battery is driven (usually about 4 AA batteries). And the amplification degree of the differential amplifier is 5
If it is doubled, the dynamic range is at most about 800 to 1000 mV in terms of input at most, so if the DC input to the differential amplifier changes suddenly due to artefacts such as body movement and electrode pad movement, There has been a problem that the output of the dynamic amplifier is saturated, which causes erroneous analysis.

Further, in the conventional electrocardiographic input circuit, the time constant of 32 seconds is realized by the first-order high-pass filter, and the cutoff frequency of the low band is realized at 0.05 Hz. Even if stabilized, it had to take more than 6 seconds for the ECG signal to return to baseline levels.
Further, a draft having a low frequency component of 0.05 Hz or more could not be canceled.

[0005]

According to the present invention, there is provided an auto drift canceling circuit of an electrocardiogram analyzing apparatus having a differential amplifier for detecting and amplifying an electrocardiogram signal. At a predetermined timing so as to fall within the input range of the differential amplifier .
Bias based on the baseline level of the ECG signal
And an auto-drift canceling circuit of the electrocardiogram analyzing apparatus, characterized in that the auto-drift canceling circuit is provided with a bias means for applying a bias voltage .

[0006]

[0007] According to the present invention, the subject wears the subject.
Differential to detect and amplify ECG signals derived from electrodes
An amplifier and an A / D converter for A / D converting the electrocardiogram signal.
A D converter and conversion data obtained by the A / D converter.
Data from the R-R interval
An R-wave detector for calculating the timing of the signal at the time of the baseline;
Of the ECG signal at the timing obtained by the wave detector
Line level to the center of the input range of the differential amplifier.
DC bias circuit and bias to the bias circuit.
An auto-drift canceling circuit for an electrocardiogram analyzing apparatus, comprising: a D / A converter that outputs a bias voltage .

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The output of the differential amplifier 1 for detecting and amplifying an electrocardiogram signal derived from the electrode worn by the subject is A / D-converted by the main amplifier 3.
It is amplified to the input level of the converter 4.

Here, signals e ₁ and e ₂ input to the inverting and non-inverting inputs of the differential amplifier 1, respectively, are e ₁ = v ₁ + E ₁ (1) v ₁ : electrocardiogram signal component E ₁ : polarization DC component due to artifact e ₂ = v ₂ + E ₂ (2) v ₂ : electrocardiogram signal component E ₂ : DC component due to polarization and artifact Eq. (1), (2), output voltage of bias circuit 2 Assuming V, the output e ₀ of the operation amplifier L is expressed by the following equation.

E = −R ₂ / R ₁ (v ₁ −v ₂ ) −R ₂ / R ₁ (E ₁ −E ₂ ) + V (3) That is, the second term of the equation (3) is a differential amplifier. Since it is considered that the drift component should be canceled from the output of No. 1, (3)
The drift is canceled when the output voltage V of the bias circuit 2 in the third term of the equation is varied and the equation (4) is satisfied.

V = R ₂ / R ₁ (E ₁ −E ₂ ) (4)

[0013] The timing T _B of the baseline of the electrocardiogram from the R wave detected in real time R wave detector 8 is generally (5) can be calculated by the formula.

[0014] _{T B (sec) = 2 /} 3T RR (sec) ... (5) (T RR = RR interval) as shown in FIG. 2, R inspection detected by the R wave detector 8 (u) And R _{RR (u-1)} and T from the previous R test (u-1)
Calculate _{B (u-1)} .

[0015] T _e value from time to time in each time of detecting the R-wave, will be updated.

[0016] Thus, elapses after detecting the R-wave T _R time, since considered the baseline of the electrocardiogram signal, detecting the difference between the center of the input range of the ECG signal level and the differential amplifier 1 at this time This makes it possible to detect the drift component of the electrocardiogram signal.

As shown in FIG. 3A, the difference V (u) between the baseline of the electrocardiogram signal and the center of the input range of the differential amplifier 1 is shown.
Is detected, and the output voltage of the bias circuit 2 in FIG. 1 is continuously varied for each heartbeat by a D / A converter so as to cancel this drift component. (B in FIG. 3) Accordingly, drift cancellation is possible as shown in C in FIG. 3, and even if the differential amplifier 1 is saturated due to a sudden artifact or the like, it can be instantaneously recovered to the baseline level.

Reference numeral 5 denotes an arithmetic processing unit (CPU).
The time interval between R waves and the distance between a drift component and the like and the baseline level are determined. Reference numeral 6 denotes a memory for temporarily storing an electrocardiogram signal output.

[0019]

As described above, according to the present invention, even if the input range of the differential amplifier exceeds the input range due to an artifact such as body motion, the input of the differential amplifier is set to be within the input range after one heartbeat. Is subjected to DC bias, so that it is less susceptible to artifacts, and has the effect of reducing erroneous analysis.

Also, since the primary filter circuit for cutting low frequency components can be eliminated, a high-precision, large-capacity capacitor (hereafter, about ± 5%) used in the primary filter and a high-precision, high-resistance (Approximately 36 MΩ ± 5%) can be eliminated, which has the effect of reducing component costs and mounting area.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between T _B and T _RR .

FIG. 3 is an embodiment of a drift cancellation method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Differential amplifier 2 DC bias circuit 3 Main amplifier 4 A / D converter 5 Operation processing unit 6 Memory 7 D / A converter 8 R wave detector A Amplifier output before drift cancellation B D / A based on drift cancellation processing Output C Amplifier output after drift cancellation

Claims (2)

(57) [Claims] 1. An auto-drift canceling circuit of an electrocardiogram analyzing apparatus having a differential amplifier for detecting and amplifying an electrocardiogram signal, wherein an auto-drift cancel circuit is provided in the differential amplifier based on the electrocardiogram signal within an input range of the differential amplifier. As you enter, the timing
A biasing means for applying a bias based on a baseline level of the electrocardiogram signal in the electrocardiogram analyzing apparatus. 2. A heart derived from an electrode mounted on a subject
A differential amplifier for detecting and amplifying an electrogram signal, and an A / D converter for A / D converting the electrocardiogram signal
And an R wave is detected from the conversion data obtained by the A / D converter.
From the RR interval at the baseline of the ECG signal.
An R-wave detecting unit for calculating the timing, and an electrocardiogram signal at the timing obtained by the R-wave detecting unit
DC biasing the baseline level at the center of the input range of the differential amplifier
Bias circuit and D / A conversion for outputting a bias voltage to the bias circuit
Auto drift cancellation circuit electrocardiogram analysis apparatus characterized by comprising a vessel.